text:
Fly-by-wire vs hydraulic systems
So, the great old argument, flyer-by-wire systems vs conventional hydraulics. I was wondering which one was better and why. Which one is safer? Pros and cons in terms of safety? Basically, I just wanted to know roughly the pros and cons of both systems.

I think you are doing a bit of confusion. FBW can use also hydraulic components, while "traditional" systems might not.

I was wondering which one was better and why.
When done equally right they are equally good.
However, FBW makes it possibly to improve the quality of control beyond what's determined by the aerodynamics (e,g, making unstable airplanes stable, or making hard-to-fly airplanes easy to fly), and making the airplane robust against malfunctioning components (e.g. stuck actuators or control surfaces), or and adverse conditions (neutralizing turbulence, wind gust, etc).
Giving computers some authority also enables the computer to correct for human error (stalling, overloading, etc), hence improves safety as well.
Which one is safer?
FBW is extremely hard to design, tune, test, and validate. Although the benefit of FBW could make the flight safer in a lot of ways, the risk that a premature FBW system could introduce is quite significant as well.
In general, although it is hard to state that an airplane equipped with FBW is inherently safer than one with conventional controls, and often times the reverse seemed true in history due to early bad track record of some FBW equipped airplanes, yet if an airplane is designed with safety as priority, FBW could offer a lot of benefits, again, if done right.


text:
How does the Mi-26 tilt its rotor like this?

I watched this video on YouTube, which shows an Mi-26 taking off with its rotor tilted forward about 45 degrees. Is the video fake or is it real, and if it is real, how does the Mi-26 do such a thing?

It's real and it's simply the blades running at the flapping hinge limits with the cyclic stick full forward.  The blade on the back is at its up limit and the one at the front at its down limit, resulting in an overall disc angle of about 30 degrees off horizontal.  It's being done to accelerate along the ground as fast as possible.  In the air, the machine's body will follow the tilt of the rotor quickly enough that this sort of angle is almost never experienced unless the pilot made a sudden extreme input in flight.
This (blades hitting flapping limits) is something that only multi-blade articulating rotors can tolerate.  You can't do that with a two blade teetering rotor because contacting the blade flapping travel stops, known as mast bumping, will break the mast.

Worth noting that this is being done in order to obtain translational lift as quickly as possible -- suggesting that this is either a heavy or high-performance takeoff.

@ZeissIkon not necessarily, the RuAF uses running takeoffs routinely because they are safer.

Im gonna pretend I know everything you said.... anyways, you mean the rotors are attached to hinges like on every door?

@ipydawa there are many different rotor hub design solutions, the Mi-26 uses a fully articulated one: image

The blades on 3+ blade rotors are traditionally attached to hinges that let them move up and down and when viewed as a whole, looks like a disc tilting this way or that.. On more modern rotors, they do away with the hinges and provide a flexible attachment using either soft bushings (called "elastomeric" bearings or bushings), or just make the blade root flexible like a fishing rod, that allows the blade to do the same thing, but the result is the same. On a two blade system, the blade going up naturally does so in coordination with its opposite partner, allowing a single hinge in the middle.

It's less than 45 degrees, I think. Probably less than 30.
There's nothing special about that. That helicopter is built with an important amount of forward cyclic. It's not the rotor head itself that tilts, but the tip-path plane is tilted with the cyclic command...

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Can helicopters have engines running while rotor blade stays stationary?
So, I was skiing sometime ago, and unfortunately, another skier got injured. So, a heli was flown up to get the injured skier. The rotor blades were stationary, but I still heard some sort of engine like sound. Does anyone know any helicopters capable of doing this sort of thing?

Yes, many helicopters (but not all) can do this. There are 2 main methods:

a clutch between engine and rotor system
for turbines only: a rotor brake on the engine output shaft. The engine contains a free turbine (i.e. a turbine stage that isn't attached to the compressor) that drives the rotor system. If you brake this shaft, the engine can run without spinning the rotors.

I can't seem to find any of these of the Bell 412 or AS350 for example. Any documentation?

Bell 412 engines: https://www.euravia.aero/engine-detail/pt6t-3df

Also, is there a term for this method of stopping blades while engine is running?

so technically I can run the engines at idle, and apply rotor brake? And does that mean that the 412 has no clutches?

The brake is called a rotor brake. The procedure would depend on the helicopter, but generally, yes I'd expect you can idle the engine and apply the rotor brake. Some rotor brakes are automatic, I see.

I guess this deos not apply to the Bell 412, just checked and the manual said that the brakes must not be on when engines are on.

It could also have been an APU running rather than the main engine.

You can even run free turbine turboprops like the PT-6 at ground idle while holding the propeller still by hand.  This is done in service.  You must not allow it to move however because if you let the free turbine start to spin the torque builds rapidly and you'll have to let it go and get out of the way.

I can't help but wonder how big a starter you'd need for a helicopter if you needed to spin the rotor blades too.

@HiddenWindshield not for the bell 412. It doesn't have an AOU to my knowledge

In all the helicopters I know the rotor brake is intended to slow down the rotor AFTER engine shutdown. There is also an RPM limit for applying the rotor brake, usually not more than 50% of the flight RPM. Applying the rotor brake on a helicopter with running engines, even at idle, would be spectacular and expensive.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What physical hardware does all the avionics on the B737NG run on? Some processor from the 1980s? Or some new and improved chip?
So, I am a tech guy and likes to fly (in sims) so, I was wondering what physical hardware powers all the 737NG's avionics and related systems (PFD, MFD, EICAS, GPWS etc). Is there an answer to this?

This question is really hard to answer. I believe there are a few thousands processors and a few million other ICs on such a big thing. Also in the 80s micro processor and micro controllers are much more fragmented than they are now.

This question doesn't mention the 737, but the answers do discuss the use of dissimilar hardware in redundant systems.

If it's using Collins Proline equipment (I think it does) it'll have early 80s microprocessors like the 8086, something like that.

This wouldn't fit as a comment but doesn't get to the processor level of your question. The 737NG/Max has a large number of avionics systems as shown by Airframer. Most of these have processors, some have multiple. In which of these are you interested?

I'm interested in the things that make/draw the EFIS stuff

OP, airframer is probably a really good place to start. Find in that list the exact model of the hardware you're considering. Then either try your luck at emailing the company directly or finding photos online and googling the chips. But I have a strong suspicion that all these will be ASICs (Application-specific integrated circuit) which might be not of use.


text:
How to disable GPWS in a 737NG just like how the Airbus can?
The Airbus planes have a feature where the GPWS can be disabled. But I cannot find any switch in the 737NG cockpit to disable the GPWS.

There is no way to totally inhibit GPWS on the B737 except by pulling the circuit breaker.
What you can do is inhibit specific modes of the GPWS. This is done via the following switches:

Source: Boeing Co.
The Below G/S switch (1) inhibits the below glide slope alerting.
Flap and Gear inhibit switches (4 and 5) allow inhibiting the "Too Low Flaps" and "Too Low Gear" alerts.
The TERR inhibit switch (6) inhibits the look-ahead terrain alerts and the terrain display on the ND.


text:
Are there any softwares that can integrate with desktop sims that accurately simulate third party EFIS retrofits?
So, are there any softwares out there that can integrate into desktop simulators, that can accurately emulate third party EFIS instruments for example, Dynon EFIS or Aspen Avionics Evolution?

If I remember right, XPlane has a pretty good G1000.

@RonBeyer yep, but let's face it, a cessna 172 with G1000 is gonna cost ya a quarter million dollars. I don't have that kind of money, and I want to retrofit. I do indeed have xplane and can testify that the G1000 is an amazingly accurate recreation.


text:
Is there a GPWS volume control in the audio control panel for the B737?
So, I was sitting in the front rows of an A320 and could obviously hear the AP disconnect. But I could not hear the GPWS altitude and RETARD callouts. I assume this is because the pilots set the GPWS to their headsets instead of speakers in the ACP. Is there a system on the 737NG?

I don't think you can set the GPWS only on the headsets, at least in the A320 I'm not aware you can do that.


text:
Where do I get the latest 737NG FCOM?
So, I went online to search for the 737 FCOM, but I can only get the FCOM from 2005. Is there a 2019 version? An updated version?

Generally, you have to pay Boeing lots of money. Or find a copy somebody uploaded to the internet, who shouldn't have. Or, buy a 737. They come included in the price when you do that (or so I've heard). Bottom line, though, it's not intended to be a public document... as the one you have probably say on the cover or on the first few pages.

@RalphJ then how do people on aviation stack exchange quote FCOM? Do they use the outdated one?

They probably were issued one by their employer -- who presumably purchased some number of Boeing jets.  Or they used an old one like you found on the internet.

@RalphJ right thanks

Just to add to the discussion, an FCOM will typically be specific to an airline. Each aircraft tends to be unique with minor variants, hence each FCOM is typically unique. However, for the sake of ease of reference, the airline with multiple orders of the same variant may have one FCOM, listing differences between individual aircraft registrations with tabulation numbers. Furthermore, an airline can work with Boeing to incorporate its own SOPs along with the AFM standard procedures to an FCOM (Volume 1).


text:
Which system on the 737NG decides the use of roll spoilers?
Which of the 737NG systems decide to use roll spoilers? FMC? Some other flight surface controller? Does it trigger when airspeed is low?

That would be the "spoiler mixer". See this document, refer to pages 3, 4 and 20.


text:
Why does the UH-1 Huey have a hump at the rear of the cabin?
Why does the Huey have this weird hump as shown in the picture? For some system? Why not remove it?

https://www.helis.com/h2/uh-1h_seats.jpg

Because the main rotor shaft and associated equipment (gearboxes) does not end at the outer fuselage skin. I am sure someone more versed in the arcane version numbers of the UH-1 will be able to weigh in regarding when the area around that "hump" was made available.

@AEheresupportsMonica Comments are not for providing partial answers.

A copy of the original image can be found here, which is about 5 'pagedowns' down this page, which has a number of other excellent Huey-model photos.
It's a bit of structure to guide the rotor forces into the rest of the airframe, it would not be good if this bit went missing.
Fwd/aft, left/right, up/down. The rotor provides the lifting forces and driving forces and these are quite concentrated around the rotor axis. Picture the airframe like an empty beer can - some panels are required to cope with the forces while remaining in shape.

Nice model. Yours?

@Freeman found it while searching for a structural image for the Huey, seems to be unclear if the original site still exists. Could not find a clear reference address for it.

Providing a source for the image would be strongly recommended, then.

It's where the main rotor transmission and control servos are housed. The forward bulkhead of the "hump" WAS the entire aft cabin bulkhead of the original Huey models. Starting with the D model (I Think) the cabin was extended around the transmission tunnel to form what are called the right and left alcoves. The original shorter body Hueys were adapted to the gunship roles.


text:
Is the 737's autopilot part of the FMS or is it a separate entity?
I was watching a tutorial about the FMS and the autopilot in the 737, and I am consfused. I come from a Cessna background, where there is no FMS, there is only the AP (autopilot).
So, is the AP a separate entity being fed info by the FMS and easily overridden by the values you input into the AP (heading, V/S, altitude)? Or is the AP under the FMS, and the FMS has full authority over the AP?

I come from a Cessna background, which there is no FMS, there is only the AP(autopilot).

I recently added the Avidyne IFD540 to my Cessna Cardinal, which bills itself as an FMS, and appears quite capable. My autopilot is connected to the DG/HSI, the IFD540 controls the autopilot thru the DG/HSI.

@CrossRoads Yeah and i fly on sims without an FMS on

People often say or write "FMS" when they mean "FMC". In the video you watched, they are probably used with specific, and distinct, meanings.  Boeing will tell you that the A/P is part of the FMS, and it can (optionally) be coupled to the FMC.  The FMC doesn't have "authority over" the A/P -- it's just one of several modes you can select. However, the A/P and the FMC both are components of the Flight Management System, or FMS. See my answer for more detail.

In Boeing terminology, the FMS, Flight Management System, is comprised of:

Flight Management Computer System (FMCS, which is essentially two FMC's, at least on the 737... other jets may have one FMC, or three)
Autopilot
AFDS (Autopilot/Flight Director System - includes the Mode Control Panel used to select autopilot modes, heading, speed, altitude, etc)
Autothrottle
GPS(s)
Inertial Reference Systems (IRS)
Two (in the 737, three in some other jets) CDU's, which are the "Control and Display Units" with a small screen display and alphanumeric keyboards, used by pilots to view, enter, and edit things such as flight routes & performance data. Many such units are now "Multifunction CDU's", or MCDU's, adding ACARS and/or CPDLC capability.

So in their terminology, the FMS is very broad and includes plenty of things, including the autopilot. The FMC, on the other hand, is the computer that stores your route, calculates the aircraft's position (based on inputs from the GPS receiver(s) + the IRS + possibly other sensors), and does all the navigation tasks. One can couple the autopilot to the FMC guidance - select LNAV and/or VNAV - or not.
It's not uncommon to hear or read "FMC" and "FMS" used interchangably, but they are in fact two separate things. The FMS (the system) includes the FMC (the computer) and the autopilot; the autopilot can be coupled to the FMC, but it is always a component of the FMS.
Sometimes you'll see a CDU referred to as "the FMC (or FMS)" since the CDU is the pilot's main interface with the FMC. But they are separate things; you can have a CDU failure with all FMC's still working, and vice versa.
Clear as mud?

Nice answer - maybe worth adding the "CDU" (Control, or Computer, Display Unit) to the list of FMS system components. This is the box with the screen and the buttons, often located on the center console, which pilots sometimes casually refer to as "the FMS" but really just another component of the system as this answer explains well.

They are separate systems, but the autopilot can be set to get guidance from the FMC (Flight Management Computer).
For lateral navigation, the autopilot can be set to follow a heading, or a VOR/LOC. It can also be set in LNAV mode, which receives guidance from the FMC.
For vertical navigation, the autopilot can be set to hold an altitude, LVL CHG based on the set speed, or follow the glideslope in APP mode. It can also be set in VNAV mode, which receives guidance from the FMC.

So there are multiple modes within VNAV?

@lpydawa that's probably a better topic for your other question

What is the ALT INTV on a 737

@lpydawa you could ask a separate question about that

They are two different systems. The autopilot receives selected inputs from the pilots, or managed inputs from the FMS. Total failure of the FMS has no impact on the autopilot which keeps following selected inputs. Total failure of the autopilot has no impacts on FMS which keeps computing the numerous data he is supposed to do such as time of arrival, fuel at destination, also the navigation data such as point to point required track, heading, optimum altitude for least fuel consumption....
As a summary they are just complementary systems.

The FMS can be thought of as an electronic equivalent to a human Navigator. The AutoPilot is an electronic equivalent to a human Pilot.
The human Pilot can listen to, or not, the human Navigator. The human Pilot can listen to, or not, the electronic Navigator. And the electronic pilot can listen to (call L/VNav), or not (called Hdg) the electronic Navigator.
Your flight, your choice.

But I heard that while the AP is "listening" to the FMS, one can change the altitude and vertical speed of the AP. Is that true? How does it interact with the FMS then?

This answer uses "FMS" to mean "FMC".  Everything described here is an accurate description of the interactions of the autopilot with the FMC. But, as my answer describes, both are part of the FMS (Flight Management System).

@lpydawa Lateral and vertical guidance are separate parts of the autopilot that can be set to different inputs, e.g. FMC to navigate along a route but manual selection of altitude.


text:
Is the callout "minimums" on the 737 used to describe DH on precision approaches
So, I have heard that decision height (DH) is used to signify the height on a precision approach which the pilot has to decide whether to continue or not.
But, in the 737, I only hear "approaching minimums" and "minimums". There is no "approaching decision height" and "decision height" callout. Is "minimums" used to describe DH too? Or is there something I'm missing?

This seems to me to be more about company SOP than about the airplane model per se. Why do you feel that this is related to the fact that it's a 737?

@aCVn maybe other planes use "decision height" callout?

DA/DH and MDA/MDH both get a callout of "minimums". The pilot is expected to know (from having briefed the approach earlier) which meaning applies. This is true for every FMS/GPS I've seen, not just the B737. On planes without this feature, one of the pilots will call out "minimums", and even a solo pilot (for smaller planes) should say the word to himself as a reminder.
While all pilots are required to understand English, it is best to assume their vocabulary is limited--especially during stressful situations or for urgent problems. Therefore, like ATC, planes use standard phrases--and as few of them as possible--to limit possible misunderstandings. If one general word can cover multiple situations, then that is preferred over having gratuitously different words for each one.


text:
What are the costs versus benefits of takeoff/landing on grass versus pavement in a light aircraft?
This question stated that landing on pavement is hard on tires compared to grass, however I don't necessarily agree with that. Even if it is true the impact on the gear and other components may outweigh the benefits to the tires. This leads to the question of what is overall lower cost for takeoff and/or landing from a maintenance perspective, grass or pavement? If that cannot be determined what are the costs and benefits of each?
This question needs limits in order to avoid being too broad, so please assume these conditions:

A tricycle gear airplane that can use either surface like a PA-28, Cessna 152/172, not something like a Mooney which is less grass friendly
The grass surface is in reasonable shape
Accident/incident costs are out of scope for the question

Slightly larger, wider and more rugged tires might be helpful for grass, you may wish to speak with "bush" pilots for possible modifications, which could also include STOL kits to further lessen the potential impacts,

Pretty simple.  Even a nicely rolled grass runway is nowhere as smooth as asphalt.
Tires on grass seem to last forever, but it wears out everything else in the gear out faster.  Oleos get worked more; they get dirtier, so it's much harder on the scrapers and seals (dust (silica particles) + hydraulic fluid on the chrome = wonderful lapping compound), etc and can be expected to start to leak sooner. Scissors linkage bushings  and wheel bearings wear faster.  Fairings and bits that flex with the gear will crack sooner.  All that sort of thing.  Impossible to quantify, although tires are cheaper than oleo overhauls.
I operate from a field with grass and pavement (actually macadam - gravel/tar) side by side and I almost always use the pavement, because on smooth grass I can feel the oleos getting worked hard and they just get a lot dirtier.
On the other hand - if it's an option, I always do my engine run up on grass, and I usually start the takeoff roll (an option where I am) on the grass about 50 ft short of the threshold.  These are propeller protection measures.  Even nice clean looking pavement will have lots of, at minimum, very small pretty much invisible stones, which are murder on your propeller when stationary or when rolling at low speed/high power.
Props make great vacuum cleaners when close to the ground and pavement is like vacuuming a tile floor while grass is like vacuuming carpet without the beater attachment doohickey.

But won't grass contain an equal amount or more dirt and micro-rocks?  I have a hard time understanding how dirt and grass is better than pavement for runups.

The grass blades diffuse and inhibit the flow entering the little tornado that forms at the bottom of the propeller disc, so that the flow can't pick up small stones. Once I started doing runups on grass, my propeller ding damage dropped probably 80%. If you are on pavement that is totally clean, fine, but usually there is gravel nearby, the very small bits of which get blown on to the pavement and are invisible. Sweep up an area near the edge of a ramp and you'll usually find lots of very small bits of limestone.


text:
Definition of a Deep Stall
I've been doing some research for a uni assignment and I noticed that the RQ-11B uses a "deep stall landing" to get back onto the ground. What I don't understand though is how this aircraft gets into a deep stall, so far every definition of a deep stall that I've seen says that for an aircraft to be in a deep stall, the horizontal stabilisers are in the wake of turbulent air from the stalled main wings. The aircraft in question has high mounted wings and a conventional tailplane, so even in straight and level flight the horizontal stabilisers are below the dirty air from the wings and so when the angle of attack is increased, the tailplane only gets further away from this airflow.
So the main question is, is there another definition of a deep stall that doesn't need the horizontal stabilisers to be in the dirty air from the stalled wing.

This is the aircraft or rather SUAV in question

https://www.aerosociety.com/media/3532/4109.pdf maybe helpful

Your case might better be called a "fully developed stall". A deep stall is characterized by a fully stalled wing, a trim point at high angle of attack plus sufficient loss of elevator control so the aircraft cannot escape by elevator commands. A fully developed stall can always be ended by pushing the nose down.

I believe you are correct and the terminology they used was incorrect. What possibly is being described is sometimes called "mushing". Some aircraft are capable of having the airspeed bleed off until the elevator is all the way up - it then mushes with a high descent rate to the ground.
I owned a Navion that would do this. If you slowly bleed the airspeed off and add full elevator it will end up with a 500-600fpm wallowing descent and severe buffeting (full aileron may be needed as the wings rock side to side).
Several Piper aircraft are also similar such as the PA-28-140 Cherokee. The Cherokee is known to run out of stabulator during flares and can pancake onto the runway - no damage but an embarrassing hard thump.
I have flown just about all the single engine and small twin engine Cessna's and none of them will do this. They have lots of elevator and are always capable of a nose dropping full stall.
Captain "Sully" Chesley Sullenberger reported he was aware the flight computer of the Airbus A320-214 did this (US Airways Flight 1549, "Miracle on the Hudson") and deliberately held the yoke all the way back and let the aircraft mush onto the Hudson River.

That makes a lot more sense, later on in the passage they described the landing a bit more. they described a 1:1 glide ratio at low speed which didn't make sense but another description of mushing I just read was ''a nose-up glide'' which sounds much more accurate. Thanks

Of course, the plane didn't do what Sully had commanded. Despite his full back stick it stopped at 9.5° pitch angle due to anti-phugoid mode programming in the control laws.

Memories of the Piper Arrow. One could do a pseudo short field technique, slowing gradually over the fence, and at the right moment, YANK the yoke full aft and it would kiss the runway just as pretty as you please.

Worth watching a video of the landing. The tail of the RQ-11 is an all moving horizontal stab, and on landing it pitches full aft, the wing clearly stalls, and it plops down at a glide slope closer to an autorotation. Reminiscent of the Spaceship One and Two. It then crashes on impact and the wing falls off, by design.


text:
How is pressure kept nearly constant in jet engine burner?
How do engineers make sure the pressure doesn't rise, but velocity does. I have no idea how that can work, please help!

I have a feeling The term "Constant Pressure" for a gas turbine engine, And the Term "Burner" used in your question, is slightly confusing to be able to clearly understand your query. Can you please specify if You Mean to ask about the Combustion Chamber where fuel and air is mixed and ignited, or the engine exhaust nozzle where there is a provision for "After Burners" in older jet engines.
Know that the Jet Engine is termed as "Constant pressure" machine in comparison with the Piston Engine Combustion, where the pressure changes with every stroke, leading to a power stroke post combustion where the actual force is generated.
When compared with Jet engine, the pressure in the Combustion Section of Jet Engine is almost constant, But before reaching Combustion Section (Through Compressor Air delivery) the pressure is made to increase with every stage of the compressors and the reason for this is to obtain high energy post combustion to generate enough force to move the turbines and to enable the Jet velocity Leaving the engine to be as high possible to be able to generate enough thrust (Newton's Third Law), and this is achieved by constructing the Engine Exhaust duct in the Convergent-Divergent shape, The reason best explained by the following paragraph from notes taken from one of the best books i have ever read,
The following is as it is from the text book, all credits to the moderators.
"In the convergent exhaust duct, the shape of the duct accelerates the gas. In a turbo-jet, the
gas flows at sub-sonic speed at low thrust levels only, at almost all levels above idle power the
exhaust velocity reaches the speed of sound in relation to the exhaust gas temperature, at this
point the nozzle is said to be ‘choked’. This means that no further increase in velocity can be
obtained unless the temperature is increased.
When the gas enters the convergent section of the convergent-divergent nozzle its velocity
increases with a corresponding fall in static pressure. The gas velocity at this point now reaches
the local speed of sound (Mach 1). As the gas flows into the divergent section it progressively
accelerates towards the open exit, the reaction to this increase in momentum is a pressure force
acting on the inside wall of the nozzle. A component of this force which acts parallel to the
longitudinal axis of the nozzle produces the further increase in thrust."
Pressure is kept Constant In the combustion chamber by not allowing the gases to escape from anywhere but to allow them to move forward only, remember there is a slight decrease in pressure during this but then the drop is considered to be negligible, and it is also made sure that the pressure at compressor delivery is high all the time thus facilitating the High to Low flow of pressure.
There are times when the air mass and pressure supposed to be in the combustion chamber returns to the compressor thus resulting into a probable surge and or a stall.
But this only happen when the compressor has problems with its blades or rotation or contamination.


text:
On the B737 When A and B systems are pretty much each other's back up for most things Why not for flaps?
Why have a seperate system for flaps? Which is alternate flaps

Do you mean an actual 2nd set of flaps, or an alternate means of extending them (such as a backup hydraulic system)?

You tagged 737, 747 and 777 while your title specifies 737. Please clarify whether you're asking about a specific aircraft type and if so, which.

Both systems power the flight controls, with manual reversion as a backup if both fail (except for the rudder -- that's backed up by the standby hydraulic system).
The A system powers the landing gear for retraction, extension, and nose wheel steering.  The backup is a mechanical release to drop the gear if the A-system fails; there is no backup to retract the landing gear without the A system.  (For those who know what the LGTU is, I'm not forgetting about it, but that's more detail than this question is asking for.) Nosewheel steering can be selected to use the B system, starting with the Next Gen 737's; before that, it wasn't backed up & you'd stop straight ahead on the runway & be towed to the gate in the event of A-system failure.
The B system powers the flaps and leading edge devices, with an electric backup that can extend and retract the flaps, and can (only) extend the leading edge devices.
Both systems can power the wheel brakes, and if both fail there is a hydraulic accumulator that gives enough brake applications that you can stop straight ahead.
There are more details, but as a big-picture overview, that's what powers what & how each is backed up.


text:
on the airbus A320 does applying rudder and tiller sum up?
on the airbus A320 while taxing, does applying rudder and tiller sum up the turn? if so where is it mentioned

on the airbus A320 while taxing, does applying rudder and tiller sum up the turn?

Yes. The pedal order is summed together with the commands from the two tillers. However, a pushbutton installed on each tiller allows the pilot to temporary exclude the rudder part of the input.

if so where is it mentioned

Usually in the FCOM under "Landing Gear". See for example page 30 here

Thank you for replying, but page 30 does not mention tiller + rudder is added. It only tells tiller n f/o and capt side is algebraically added

@Deepak there is a diagram on the next page


text:
Can a Continuous Descent Final Approach (CDFA) be carried out if there is no final approach fix?
Is it possible to carry out a CDFA approach if there is no defined final approach fix mentioned on the instrument approach chart?

Just to add some extra context to this question, internationally the FAF, FAP, CDFA, CDA may differ from how they are recognised by the FAA. A good few paragraphs on this are found in the wikipedia page “Final Approach” - Section “Final Approach Fix and Final Approach Point” https://en.wikipedia.org/wiki/Final_approach#Final_approach_fix_(FAF)and_final_approach_point(FAP)

CDFA is possible. The VDA is published after the fix from which it applies. In this case, that is AMBAZ. The VDA calculation has nothing to do with the MAP location or the MDA.
See the FAA’s AC 120-108A that was just released in March ‘23.

For the KLAL VOR 27 approach, it is possible to perform a CDFA type approach.  On these types of approaches with a procedure turn, the FAF is defined as alignment with the final approach course after the procedure turn.
There is a DME distance available and a descent angle on the chart. The descent angle suggests approximately 300 FT/NM descent.  The TDZE is 142 and the TCH is 45 or a threshold crossing altitude of 187.
If you were at 2,000 FT MSL just finishing up the procedure turn a descent should be made at (2000 - 187) / 300 = 6.0DME is where you start the descent.
But notice, that puts you on a descent path to the MAP after the runway begins and you may need to circle if you complete the CDFA and can see the runway.
It is best to dive and drive this type of approach so you can be in a position to land when you break out of the clouds.  Especially since the runway will be to your right and not directly in front of you.

You’re not flying a CDFA if you’re using 6 DME to begin your descent. That is not at all how you are supposed to use the information on the chart.


text:
Is lift/drag the same as coefficient of lift/coefficient of drag?
I see it being used interchangeably (for example by Airfoil Tools Fusion360 AddIn), so can I just pick an airfoil from the airfoiltools database with a certain CL/CD for my aircraft and assume L/D is the same?
An example airfoil from the database: clarky-il
(I know there is induced drag as well, which is not calculated in the databse)
I know the formulas, so it makes sense to me. Just want to verify there is not something I am not aware of, in case I want to calculate the lift depending on the angle of attack.

Yes. Lift and Drag are both obtained by multiplying the CL & CD by the same factors (1/2 rho V^2 S); the ratio L/D cancels out those factors, leaving CL/CD.

I thought a bit more about it and now it seems so obvious. Thanks for verifying it.


text:
Why are birdlike airfoils not used?
Here are two airfoils (lets focus on Re 100,000):

SD7043-il which is simple to build and has a glide ratio of about 60
e376-il a birdlike and much harder to build if using paper or similar due to the hollow inside but claims to have a glide ratio of about 105

I have never seen such birdlike airfoils on an aircraft (RC or other). Is it because of construction difficulties?

You might want to start by defining what you mean by "birdlike airfoils." Never heard that before.

Can you define what you mean by "birdlike airfoils"? Neither of the two you linked to look very birdlike to me. To me, the definition of a "birdlike airfoil" is one that can radically change its shape multiple times a second, and I don't see that happening in the ones you linked to.

To me a birdlike airfoil is a high camber, thin hollow underside airfoil. Here is an example: https://www.semanticscholar.org/paper/The-Flight-of-Albatross%E2%80%94How-to-Transform-It-into-Pfeifhofer-Tributsch/43d5bf0d265540ee9bb8a378cb3fc0524d9827de/figure/3

Excuse an amateur but what is the significant difference between them? In my amateurish eyes they look very similar?

@d-b The ones I posted in the link are all birdlike airfoils (from real birds). The e376 is very thin and has high camber like the bird wings. However the SD7043 is compared to the e376 very thick and has very little camber.

Early biplanes did use similar airfoils. Not as extreme as the Eppler 376, but still very thin and highly cambered.
When Otto Lilienthal started his glider experiments, he tried to copy storks. He experimented with different airfoil shapes by using exchangeable ribs on the gliders and by testing model wings on a rotation test stand (Rundlaufapparat). There he discovered that thick airfoils with a blunt nose were actually better than the thin, birdlike airfoils he had used so far. But he didn't believe his own results and continued with birdlike airfoils.

Farman-Voisin biplane, 1907 (picture source).
The same happened with all other airplane designers until 1915, when scientific work started to influence airplane designs. The highly cambered airfoil works very well in a very small range of angles of attack when the local direction of flow is parallel to the local contour of its nose. But while birds can adjust the camber and area of their wings, airplanes of those times could not. In order to combine fast flight with high lift for take-off and landing, the thick airfoil is better.
While birds are small enough to structurally get away with thin wings, the much larger man-carrying airplanes need the thicker wings to accommodate their bending loads without bracing. Scaling laws show that loads grow faster with size than the dimensions do and only thicker wings make the unbraced, cantilever designs necessary for efficient transportation possible.

Heron in flight (picture source). This picture shows nicely that 90% of the area is feathers, so a thick wing becomes impossible for birds.
Birds cannot be hollow inside, except for hollow bones. So they have no choice of using thick wings - they have to work with thin wings and adjust camber and wing area to the flight conditions. Being much larger, airplanes need thick wings for aerodynamic and structural efficiency.

Though there have been fairly modern airplanes with very thin wings, e.g. the F-104: https://en.wikipedia.org/wiki/Lockheed_F-104_Starfighter#Design

Your links led me to a streamline of other answers you gave. Interesting stuff!

Great point about scaling laws, I think this is something not commonly understood and it affects numerous physical phenomena which people think their intuition should explain.

@jamesqf Right, all supersonic aircraft use very thin airfoils. But those have very little camber, too. This optimizes the design for supersonic flights, something that cannot be learned from birds.

Also, birds use their wings for propulsion as well as lift so necessarily their wings must be completely different.  The idea that we can learn anything new about aircraft design from observing birds went out of vogue at least 100 years ago.  Unless someone wants to step back in time and try building a wing-flapping ultralight!  (There's plenty of black and white footage showing what NOT to do...)

"a thick wing becomes impossible for birds" They could have one layer of feathers for the top of the wing, and a second one for the bottom of the wing, creating a thick, hollow wing.

@nick012000 They do have this - see the darker feather area of the heron wing behind the bone and muscle part at the leading edge. But it doesn't extend far, just enough to have some transition to the single-layer feather area. Nature decided it's not worth to have this double-feather area extend all the way to the back. It makes the wing heavier than necessary.

@jamesqf F-104: German dark joke long ago. "Q How do you acquire A Starfighter? A: Buy a plot of land and wait". // I saw the only one I've seen in a park in Taichung - looking out across the Formosa strait and dreaming of days of past glory. Around here

@PeterKämpf "This optimizes the design for supersonic flights, something that cannot be learned from birds." Except maybe the really scary falcons from xkcd. Or maybe these falcons or these eagles.

@Russell McMaho:  Apparently there are a number of privately owned examples flying, e.g. https://generalaviationnews.com/2018/03/03/f-104-flight-training-takes-off-kennedy-space-center/  There used to be a privately owned one parked at the Grass Valley (California) airport, though I haven't been there in maybe 20 years.

The short answer without the science is.. Too much drag !!
if you copied the profile of a birds airfoil, it would be in practise on an airplane, very high lift but very high drag.. The drag would probably be so bad that you would struggle to pass 40-50 mph..  The reason it works on a birds wing is very simple, wing area.. If a bird wants to go fast they tuck the wings in, if they want to go slow they stretch them out.. They can also modify the profile slightly depending on the bird of course done aka wing warping..
Bottom line is its way to much drag for airplanes..

All of these answers get the actual physics wrong.
The difference in thick vs. thin airfoils isn't about structural scaling.  It is about Reynolds number.
Birds operate at much lower Reynolds number than even the smallest and slowest person carrying aircraft do.  Stall behavior is strongly related to leading edge radius and Reynolds number.
Some of the early tests were also done at very low Reynolds number -- confirming the use of bird-like airfoils.  The earliest aircraft were extremely slow -- operating at Reynolds numbers that almost matched the existing data.  As aircraft got faster (largely through WWI), our understanding of aerodynamics improved and thick airfoils were adopted.
Notice that bird airfoils are nothing like insect airfoils (pure flat plate).  Again, insects operate at very different Reynolds (much lower) number than birds do.

Perhaps you could share which bit of the accepted answer gets the physics wrong?

insect airfoils aren't exactly flat and do operate akin to stepped airfoils such as Kline-Fogelman family

@user721108 Fair enough.  Their aerodynamic differences are still best explained by differing Reynolds number.  (though they are also in a very different structural regime).

@PartyArk  The accepted answer is a lovely historical account that largely gets things right.  However, it does not discuss the physics in general.  When it does, it focuses on structural scaling (squared cube law type stuff) to explain why thick airfoils are needed for airplanes vs. thin for birds.  The history story is right, but it leaves out the aerodynamic performance difference -- which is all due to Reynolds number.

Thank you - maybe a better word then would be 'incomplete' rather than 'wrong'.

"All of these answers get the actual physics wrong" I don't think so, especially the chosen one... Your answer has a different point of view, that's all. For sure not more nor less correct than the other ones...

@PartyArk   I believe Anderson's 'History of Aerodynamics' has a good treatment of this subject -- but I'm going from memory here.
The thin bird-like airfoils of early WWI had poor stall characteristics at high Reynolds number -- not just lower clmax, but also abrupt leading edge stall instead of trailing edge stall.  This behavior is starkly different from the low Re behavior that birds get.

@sophit The thin foils did present structural challenges -- lots of struts and wires and forced to a biplane configuration.  However, those disadvantages were understood and were accepted because the airfoils were believed superior -- i.e. the penalty of the thin structure was accepted early on because of the misunderstanding of Reynolds number.
Later in the war, as aerodynamic understanding improved, aircraft moved to thicker airfoils -- and they got better dogfighting turn performance by the increased turning performance from the better stall behavior.

The thicker airfoils allowed some of the struts and wires to be removed -- reduced drag helped increase speeds.  Eventually they were able to move to monoplanes.
The aerodynamics of the thicker airfoils from better understanding of flow allowed the move away from the structural penalty of thin airfoils.

@RobMcDonald: most probably we studied on the same books and papers so I already know the theory behind. I just highlighted that you can give a very good answer even without saying that all the other ones are wrong... And actually all answers miss the real (historical and physical) point which is the need for speed and the parallel availability of more and more powerful engines: this is what drove the change from very thin high cambered airfoil toward the present shape


text:
What do multiple slashes in METAR mean?
The current METAR for Stanstead in the UK says:

EGSS 031520Z AUTO 29011KT 9999 FEW021/// //////TCU 07/02 Q1022

I do not know how to interpret the /// and //////. From what I remember multiple slashes means that data is missing, however the data in this metar seems complete.

What does FEW021/// mean?
TCU means Towering Cumulous, which makes sense, but what do the leading ////// mean in this context?

Complete, unless you want to know the height of base of those TCU's!
The bulk of the information you're after can be found in AIS-GEN 3.5 Section 10.17 - AUTO METAR coding
In describing the coding used by automated systems, it gives this example

NNNhhh/// Cloud detected, but it is unknown whether it is a convective cloud type (ie TCU or CB)

And this one

//////TCU Towering Cumulus detected, but no information on its height or cloud cover is available

Which more-or-less covers your two questions, I hope.

It means that the report is from an automated weather station and information from sensors are not available for visibility etc.
From AIP Australia:

12.20.1 A report from a fully automated AWS that does not include information from sensors for visibility, weather or cloud will report ////, // or ////// respectively in lieu of these parameters.

For this METAR, it can be seen that there are a few clouds at 2100 (with further data missing) and there is towering cumulus, with further data (cloud amount and height missing). For example, decoding this METAR at flightutilities.com gives:

Location: EGSS
LONDON - STANSTED - ENGLAND
Report emitted the day: 03, time 15:20 UTC
Wednesday 3 February 2016 20:50 local time.
Report is fully automated, with no human intervention or oversight.
Wind: True direction = 290 degrees, speed: 11 knots (20 km/h) (6 m/s).
Minimum horizontal visibility: 10 km or more.
Clouds: A few (1-2 oktas), at 2100 feet above aerodrome level (640 meters), but it is unknown whether it is a convective cloud type.
Clouds: cloud type not reported, the cloud base is under the station level or not reported, towering cumulus.
Temperature: 7 degrees Celsius (45 Fahrenheit). Dewpoint: 2 degrees Celsius (36 Fahrenheit). Relative humidity 70.47 %. Wind Chill: 4 degrees Celsius (38 Fahrenheit).
QNH (Sea-level pressure): 1022 hPa (30.18 inches).

(I've removed some data and added emphasis).

Ooh I like that Flight Utilities link - I'm terrible at deciphering METAR, that should help, thanks. (Edit: Oh, it's too clever and actually goes to look up the METAR rather than purely decoding it, damn - useful, but I was hoping to use it a little more literally. Still handy though)

It looks like that reference for Australia doesn't match how the slashes are used in the U.K. (both instances of the slashes in the question are cloud-related and the triple slash isn't even listed as an option in that AIP quote, for example.)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How does ATC handle a controller with psychological trauma?
I've finally got around to watching Breaking Bad, (spoiler alert) in the last episode of season 2 a bereaved ATC controller accidentally causes a mid-air collision.
I am not asking whether the actual collision scenario was realistic, my question is whether the scenario of a controller with a very recent tragic loss being alone at the console is realistic. How would FAA ATC management deal with a controller who'd recently suffered a bereavement like loss of a loved one or some other sort of psychological trauma? What is the route back to work: is there a mandatory off-work policy, psychological assessment or supervision period?
I've limited this to FAA in order to keep it from being overly broad, I'm sure practices vary widely.

To my knowledge there is no automatic loss of medical clearance following a death in the family. The relevant order is JO 3930.3, current version C. From Chapter 3 Section 1 Medical Status we have the following paragraph:

3. Interim Medical Condition of an ATCS. Illnesses, injuries, or other medical conditions that could affect the employee’s eligibility for medical clearance may occur between periodic examinations.
a. When an ATO Air Traffic management official becomes aware of an ATCS’s absence due to a medical condition, treatment, or drug/alcohol related incident, the Air Traffic management official must promptly inform the FS so that a determination may be made whether the illness or injury affects the ATCSs medical status.
b. An ATCS must report to the FS office the following as soon as he/she becomes aware of the condition, but in any event before performing safety-related duties:

Any assessment or treatment of injuries, illness or other medical conditions by a health professional, except for conditions as noted in Chapter 1 paragraph 9.e,
Any occupationally related injury or illness, and
Any conduct that represents a violation under a DOT or FAA Order such as DOT Order 3910.1 series.

c. Air Traffic management must inform the FS when an ATCS receives medical attention and may request an opinion from the FS regarding the medical status of the ATCS.
d. The FS evaluates available information, obtains additional data if needed, and arranges for examinations or further evaluations as required to make a medical status determination in accordance with this Order.

None of that explicitly accounts for grief but either the controller themselves or management could decide the controller's actions and mental state warrant reporting to the flight surgeon.
There are various ways for a controller to try to deal with grief and loss, for example the FAA contracts with Magellan Health as the agency's Employee Assistance Program provider (I believe up to eight counseling sessions per year are allowed for free), and NATCA (the controllers' union) provides a peer-to-peer service called CISM. The EAP is supposed to be confidential but can pass information to the agency if they suspect the employee has a substance abuse problem.
The collective bargaining agreement provides that up to ten days of annual leave or leave without pay shall be granted (at the discretion of the employee) if there is a death in the employee's family. So you get two weeks off guaranteed, if you want it, but that doesn't really pertain to your medical clearance.
The realistic answer is, if the controller really needs to talk to a therapist or counselor about what they're feeling, they have three options:

Keep it bottled up inside,
Visit an out-of-network therapist, pay out of pocket, and use a fake name if possible, or
Visit an in-network therapist, create an official record of the visit, report it to the flight surgeon (because they'll be really mad if you don't report it and they find out anyway) and hope you can successfully argue to get your medical back after it gets pulled.

If the medical never gets pulled, I don't think there is any additional supervision mandated. But the controller's coworkers will probably keep an eye on them, and if management is on the ball they probably will as well.
If the medical does get pulled, and it takes too long to get it back, the controller will first lose currency and then proficiency on the control positions they've been certified for, depending on how long since they last worked. If they lose currency they will need to re-take a "certification ride" where they control for a decent amount of time while a supervisor is plugged in with them to make sure they still know what they're doing. If they lose proficiency they will probably need to go through their facility's training process again.

In general the likelihood of someone being completely alone in the operational quarters is relatively small, at least at a larger facility like ABQ. Perhaps on the overnight shift there will be just one person in the tower cab and one in the radar room, but generally more than one control position will be open in each area, and higher-up management are generally strict about having a separate supervisory position open as well. (Each operational area needs a supervisor position at all times, but this position doesn't have to be a management supervisor—controllers who are so certified may work the supervisor's desk—and in times of low staffing the supervisor position may be combined with any given control position.)

"But the controller's coworkers will probably keep an eye on them, and if management is on the ball they probably will as well." One would like to think that this is (and was intended to be) in the "I have compassion for a coworker/friend/fellow human being who has just gone through a tough event" kind of "keep an eye on", not a "suspect that this guy is gonna screw up" kind of "keep an eye on".


text:
Do airplanes with fixed gear usually turn upside down during water landing?
During discussion about emergency landing on water in this YouTube video (4:00) the flight instructor said:

"...the problem with these airplanes with a fixed gear, you're usually
  going to be upside down".

Is it really like this? If so, is there any water landing technique which could minimize the risk?

Depends on the airplane.  I recall reading about a guy flying across from the Aleutians to Japan, in a Piper Super Cub of all things, and he had to ditch it for whatever reason, which he was able to do next to a freighter.
To his surprise, it didn't flip over but kind of submarined, stopped, then popped to the surface nose down but upright. It's possible being a taildragger helped.  I think tricycle gear airplanes would be more prone to flipping right over because the pitching moment from water contact is a little stronger with 3 gears hanging down vs two.
I expect though, that if you surveyed ditchings you would find some do and some don't.  Pitching moment from water contact, elevator effectiveness in resisting the pitching,  amount of up elevator at water contact, speed at water contact, maybe the surface contours of the fuselage could promote it or inhibit it, all kinds of variables.
As xxavier says, it would be prudent to assume you are going to flip over, and if you don't, bonus.

It is situational.  Locally there have been three Cessna ditchings that I have first hand knowledge of.  One of them resulted in an inversion.  The other two did not.
The general wisdom seems to be that high wing aircraft are more likely to upset than low wing aircraft.  I do not know what NSTB statistics are.
I am sure there are factors such as: vertical CG, AOA and or the attitide hitting the water, glassy water vs rough conditions, wind, gear dressings (tires, pants) etc.  At one time, probably 18 or so years ago, I saw a aeronautical engineering student's work on a simulation to model the likelihood of upsets using various commuter and short haul aircraft models, and what might happen in a ditching.  I have not seen anything more definitive since.
In the interim, if you plan on over water flights, the FAA safety seminar where one practices egress inverted and underwater, is a nice seminar.  I have taken it twice, and I learn as much the second time around as I did the first. Fortunately, I have only had to demonstrate my skills in a high school swimming pool.
Not all water is as friendly as the Hudson during daylight hours.

The answer is in the torque created by protruding landing gear when they strike the water first with any forward motion relative to the landing surface.  Water is much denser than air, so the drag created at the end of the lever arm of the landing gear easily flips the plane over.
Thus is why, if possible, water ditching is done gear up with the intent of "belly flopping" the aircraft onto the water. Low wings and fuselage can absorb the impact over a greater area and will generally have a lower center of gravity, but GREAT CARE must be taken not to catch a wing tip first as this (also by torque) will cartwheel the aircraft.  High wings also stand a greater chance of remaining upright with gear up, if possible.
The best way is to reduce the ground (water) speed as much as possible by landing into the wind and holding the nose up as long as possible, applying full up elevator on contact.
Full flaps should be used for the lowest landing speed possible.
As @ mongo said, training to escape an inverted aircraft in water is great life insurance, and would be worth the time in any type of aircraft.

In theory, for small airplanes with a very low stall speed, and with the help of a kind headwind, you may slow the plane down so much that the impact with the water may be almost vertical. But that's the theory... In practice, you should be ready to exit the cockpit inverted and underwater...

While this may be true, it doesn't really answer OP's question "Do...turn upside down during water landing?"


text:
Aviation Statistics Sources
Are there any online, publicly available sources of aviation statistics, like:

number of manufactured aircrafts by type and year
number of registered aircrafts by type and year
number of aircraft incidents by type and year
etc.

I'm aware of Annual Reports of General Aviation Manufacturers Association, but this data is just for general aviation and it doesn't contain numbers before year 1990.

I don't think resources location is in the scope as defined by the help center

You wont find a single source for any of these things but you can find some of the info form fairly reliable sources:

The NTSB publishes accident data by type and year but this is only for US accidents or accidents involving US aircraft that they can investigate overseas.
The FAA allows you to lookup by make and model and would allow to get some info on registered aircraft but again only for the US.
ICAO also lists their final reports online which give a more global picture of whats going on but you will still need to combine all the data. They also offer some rolled up stats.

All of these sources generally can get spotty before the 80's for a few reasons. A lot of those reports only existed on paper and are still being digitized so results are intermittent. Official governing bodies started at different times around the globe and even paper reporting took time to standardize, accidents that pre-date that may have gotten lost in the mix.


text:
Question about flying around hurricane
I'm supposed to fly from NYC to Jacksonville on Friday afternoon. If the forecast for Hurricane Florence holds, the storm should be somewhere over the Carolinas at that point. With neither NYC or Jax being directly impacted, can commercial airliners fly around the hurricane? Would it be likely that our flight would be cancelled/delayed because of a major hurricane being in the flight path? Thanks

Have you asked your airline?  I bet they tell you "we won't know until at least Thursday."

Hurricanes move en masse pretty slow compared to a jet airliner.
Heck even compared to a small plane. It is not a problem to fly a path around them to avoid them.  Eventually the winds and rain will impact local travel, but the hurricane must be 'pretty close' for that - how close will depend on the aircraft size.  Wind/Rain/ceilings will impact small aircraft sooner than large jet airlines that fly hundreds of miles faster.


text:
How do you calculate the range of a VHF transmitter that is on-board an aircraft?
I'm trying to calculate the range of a VHF transmitter on an aircraft output power 50W, frequency 130MHz, and reciever sensitivity of -100dBm.
The calculations I have made give me ridiculously high numbers in the regions of thousands of Kilometres. The formula I used for this is as follows:

Is there perhaps a different formula that I am not aware of?

What are the values you're using for the rest of the variables? Gt and Pr would be needed to compute the R value. Is your wavelength in meters, or in what unit of measure?

Antenna and recievers gain can be treated as negligible i.e. 1 in each case. The recieved power is -100dBm. I am getting crazy values when I utilise the above formula since -100dBm the lowest signap strenth that the reciever should pick up. But that translates into 0.1pW which then means ghe distances is far greater. How do I factor in line of sight and the curvature of the earth?

VHF radio transmissions are primarily limited by line of sight. The formula for this is d = 1.23 * (√h1 + √h2) where h1 and h2 are the altitude s in feet, and d is the max range in miles.

This is a treshold distance. Beyond "d" you will not receive any signal (and this is true for frequencyes higher than atmosphear plasma resonance frequency). You can't calculate the received power using this equation. The power depends from the medium losses, the antenna qualities, the frequency and, of course, from distance.


text:
Can pressurized aircraft be flown without pressurizing
Are there any pressurized aircraft models which can also be flown without pressurizing the cabin?
For example, if there were a short ferry flight, or a flight where the aircraft never got high enough for pressurization to be necessary, is it possible to have the aircraft remain unpressurized?

This question is similar to: Can airliners take off, cruise and land while unpressurized?

Yes you simply fly with the pressurization system set to a mode that holds the outflow valve open so the air conditioning air being pumped in can't "inflate" the cabin; it all just goes overboard.  Most transport aircraft have a specific QRH procedure for "unpressurized flight", which among other things, limits the maximum altitude to 10000 ft, the altitude that most people can tolerate without any risk of becoming hypoxic.
Airlines will ferry airplanes from place to place unpressurized for maintenance.  An airliner may also be forced to descend due to a pressurization problem, and they will descend to 10000 ft and may even continue to destination at that altitude, weather permitting, as long as there aren't other problems present that dictate an immediate diversion.


text:
If an airline purchases an aircraft, do they have to/feel compelled to change the livery?
If an airline purchases a used commercial aircraft, which would be painted in the livery of its previous owner, would the new airline ever be required (by law) to re-paint the aircraft in their own livery?
I am also curious what happens if a private individual were to purchase a used aircraft from an airline, again painted in their livery. Would they be allowed to fly it for some time still bearing the livery of the airline that used to own it?
If there is no law regarding this, then is there a general practice? I.e. most airlines would just keep the old livery until the airplane is due to be re-painted?

Just as a matter of information, the livery of an aircraft is sometimes changed for a short period for contractual purposes. For example, the last 747 carrier I flew for painted the aircraft on a 3 month Hajj contract in the livery of the national carrier we were flying the Hajj for. The previous 747 carrier I flew for had two freighters on contract to another national carrier, and the aircraft were painted in the livery of the national carriers.

I recently saw photos of some aircraft still flying with air Berlin livery in a question here, which is defunct now. I believe it depends on what youre doing, if you're not acting as the company in livery nobody would care because you're basically advertising for them. For example look at Nissan.com its pretty much same story. Related question : https://aviation.stackexchange.com/questions/54857/why-is-there-still-an-air-berlin-branded-plane-operating-as-of-sep-5th-2018

Thats really interesting @Terry, the reason I asked was because I was under the impression that painting an aircraft (especially big jets, like the 747) was a huge, laborious process that would only be undertaken if it was absolutely necessary, when the aircraft was due to be re-painted anyway.
Although it sounds like I was mistaken and airplanes are quite routinely re-painted depending on what kinds of operations they're being used for at the time. Do you know if re-painting was seen as something routine to do quite often at the carriers you worked for?
Really interesting information!

@AliErdem I have heard about cases like this too, where an airline changes its livery, but older planes they have, which are still painted in the old livery is not re-painted. I believe one of the big American airlines also recently changed its logo, but a few of their older planes retain the old one!

@Ardysix Circumstances can make the cost of repainting justifiable. Tower Air was a Jewish-owned carrier whose primary scheduled route was JFK-Tel Aviv and they were known for that. Thus a contract with Garuda Indonesia to carry Muslim pilgrims to Mecca in Saudi Arabia (technically still at war with Israel) required the expense of replacing the large Tower Air lettering with Garuda Indonesia. In the second instance 2 Evergreen International 747s got the full Air India livery for an extended contract, Air India being very sensitive about not being able to keep their 747s running.

It's not a cheap process (as is taking the aircraft out of service while the job is done), but the definition "absolutely necessary" can be as simple as "whoever is paying for it says that it's necessary."

Yes - logos, trading names, liveries etc are all covered by trademark and you would need permission from the trademark owner to use them yourself. Besides, the schemes are good marketing so a commercial operator would want their own livery on it as soon as practical.

Trademark, not copyright.

It just isn't true that logos and trading names are protected by copyright. Logos can be protected by copyright if they're complicated enough; names are never protected by copyright.

@TannerSwett I wrote copyright but meant trademark, which definitely protects names.

Thats really interesting, its very reasonable though that copyright law would come into effect, and I completely agree that the new owner would want their logo on the plane ASAP for the advertising and marketing!

They sold the airplane to you with their livery on it. Without a stipulation otherwise, doesn't that imply permission to use it? Otherwise I'd have to start removing all of the branding from all of my clothing as well.

@TomvanderZanden I could easily imagine that a standard sales contract in the airline industry would contain an explicit stipulation that the buyer is obliged to remove the seller's livery within some reasonable time. (But I have no hard knowledge of this).

@tom using your example, the branding of your clothing would relate to Boeing or Airbus, just like if it was a soccer shirt it would relate to Nike or Adidas, while the soccer team shield would relate to the livery. I don't think it should even be in the contract, as flying with the liveries of a company that is not yours would probably qualify for impersonation, not only for the brand and logo itself, but also for the callsign

I'm with Tom and Henning. It just make sense that the seller itself has to repaint it before handing over the plan or a repaint at some point in future is part of the sales contract.

This answer is not consistent with the "trademark first sale" doctrine.

Under the "trademark first sale doctrine" in the USA, if an aircraft is sold with trademarked livery, the buyer would have the right to operate the aircraft without removing the livery, including operating the aircraft with paying passengers, and to resell the aircraft with the livery still in place.  The buyer would not have the right to use a trademark in new marketing materials, so printing the image of the trademarked livery on advertisements or a different aircraft would not be okay.
The aircraft seller, previous operator, and trademark holder could all be separate companies because there are leasing and licensing agreeements.
The buyer could waive their rights in a sales contract.  The seller could remove the livery before selling.
The normal purpose of livery is marketing, so normally a commercial operator will change the livery voluntarily.
IANAL.


text:
What are the technical details of how airline seats are installed on an airliner?
What are the technical details of how airline seats are installed on an airliner? The step by step.  Not made how they are installed.

Are you asking about crew or passenger seats? And there are several types of each.

@fooot, I am referring to passenger seats.

Economy seats are removed (and installed) row by row. The row of seats (typically 2 - 5 individual seats) are bolted to a track on the airframe floor. You can see them being removed in this video (~18:30) during a D-Check. The rows are usually held in place with bolts, often in the corners and where seats meet. You can see an example bolt pattern here.
Modern First class seats (the more sophisticated individual ones) will be removed one at a time often with the whole entertainment center around them. The above linked video also shows this.
And, of course, installation is the reverse of removal.

On most western jets, there are seat-tracks where the seats are fitted. The tracks are fixed to the floor beams and while the seats are fixed to this track, they are not rigidly fixed. This is to allow slight movement when the aircraft flexes. If they were rigidly fixed they would cause localized stress which is undesirable. In fact most of the stuff in the aircraft is not fixed rigidly to the airframe .. Overhead racks and bulkheads included.
The part on of the seat which interfaces with the rack has a circular part which corresponds to a cut-out in the seat-track. You fit this part in and then slide it so that its in between two cutouts. A bolt is then used to prevent further movement.
Similar tracks are used on aircraft ULDs (containers and pallets).


text:
What is this squawk 7777 target at an altitude of 62,700' over Germany?
Can anyone shed any light as to what this is (circled in white)?

This is a military test transponder, not a real aircraft. The callsign GAFTT08 stands for German Air Force Test Transponder 08. When you zoom in on the map, you can see the reconstructed position move in a pattern around the fixed true position:

(adsbexchange.com)
As far as I can tell, the military does not publicly say what exactly they are doing here. The only sources I could find are from forums:

GAFTTxx = German Air Force Test Transponder

(flugzeugforum.de)

German Air Force Test Transponder. So not an aircraft, not a drone. Don’t know why it is online all the time, but it is. Sometimes over Würzburg, sometimes over Ingolstadt.

(forum.scramble.nl)
Additionally, the squawk code of 7777 is used in Germany for fixed test transponders according to Wikipedia (thanks to ymb1 for pointing this out):

7777 US, Germany, Belgium, Netherlands: Non-discrete code used by fixed test transponders (RABMs) to check correctness of radar stations (BITE)

(List of transponder codes - Wikipedia)
This is also confirmed by the following ICAO definition:

Code 7700 is reserved for recognizing an aircraft
  in emergency. (Codes 7711 to 7717 and 7721 to 7727 are
  reserved for SAR operations and code 7777 for monitoring
  the ground transponder.)

(ICAO - SSR CODE ASSIGNMENT SYSTEM, emphasis mine)

Test transponders are used to verify the accuracy of radar data. They are known to always be in a fixed position (the movement you see is probably due to inaccuracy of ADS-B Exchange). Controllers or technicians will periodically check that the reply from the test transponder is within a defined range of the expected position.

It is not moving in a pattern, the multilateration system used to calculate its position has pattern in it's position errors.

@J.Hougaard & DeltaLima Thanks, I clarified in the answer what the movement is.

It is a test transponder for the German Air force. According to Wikipedia, it is a test for the friend or foe identification system. So, basically they are testing technology to identify aircraft, so they can aviod friendly fire in battle situations. It is not a real aircraft.

I don't see "test transponder" or "7777" mentioned anywhere in that Wikipedia article. Could you clarify what makes you think it has anything to do with an IFF system?

@J.Hougaard scroll down -> squawk code -> scroll down .. find
"7777 US, Germany, Belgium, Netherlands Non-discrete code used by fixed test transponders (RABMs) to check correctness of radar stations (BITE)"

This should be the wiki page linked - people shouldn't have to follow the breadcrumbs.

@eagle275 Still doesn't appear to have anything to do with an IFF system

And it does not have. Military transponders are different. This is purely for ATC (even if used by military too).

authors: Vladimir F Героям слава


text:
How are V speeds spoken?
How are V speeds spoken? --Research for my novel.
Is it the V and the number or letter notation or is there something more to it?
The Wikipedia Page on V Speeds does not delve into the subject matter.  I did search the search box, prior to submitting, but nothing has come up.
Please don't get angry by my question or restrict my learning.  I can always go to a better source--I got a message some of my past questions were not well received.

Related: What do jet pilots say during the takeoff as they are speeding down the runway?

If you are researching for a story, you probably have a scene or plot point in mind. It would improve the question if you outlined it—the question would be easier to understand and we could focus on the aspects relevant to that scene or plot and possibly point out other aspects you should mind.

It Depends on the speed, and in some cases the context it is being announced or discussed, different pilots may also call things out differently depending on op specs or simply the way they are trained.
V1 is typically announced as "V One"
I typically announce V4 as "Trimming for XXX Knots"
Vfe for me is typically "in the white arc, deploying flaps"
Vr is typically announced as just "rotate"
Vx and Vy are usually discussed as such or some times as "pitch for best angle" or "pitch for best rate"

Some of the V speeds are never really announced but important to know. V speed numbers help define the operational envelope of an aircraft but are not always announced or even relevant to announce. For example unless you are in a really bad situation its unlikely you are ever going to announce Vne out loud but its a very important speed to know (and avoid).

Curious to learn what aircraft it is you fly - I would have naively assumed there can’t be many where V1 is calculated (my mind associates: big multi-engine) but where a single white arc is sufficient for all flap settings (my mind associates: light aircraft). Standing by to learn something!

@CptReynolds I fly a lowly Piper Archer. All of these are call outs for me accept V1 that note is on things I have seen for bigger operations as you note. All the other call outs are things I announce. However I generally call out every 10 knots on takeoff roll up to my rotation speed of ~65 Kts. It saved me just last weekend, an inop ASI lead to an aborted takeoff which was a first for me.

Thanks very much for the explanation. Good job on catching the ASI!

These are the standard calls you use on the RJ. Pilot Not Flying is pilot monitoring and Pilot Flying is pilot on the controls. Typical of jets:
PNF: "80 kts" (or 90 or 100 depending on jet - the low energy/high energy braking threshold for rejects)  PF says "check".
PNF: "V1" (passing decision speed)
PNF: "Rotate" (passing Vr.  Often V1 and Vr are the same, or so close together and the jet accelerating so fast, you pretty much say them as one word, "Veeonerotate")
PNF: "Positive rate" (when the vertical speed indicator comes off zero - PF calls "gear up")
PF: "Speed mode"  (When passing V2 + 10 or 20 kt - PNF selects speed mode on flight director which gives pitch commands to maintain the set speed)
PF: "Heading mode" (if ATC has provided a departure heading - PNF selects HDG on flight director, which gives bank commands to maintain the set heading)  OR
PF: "Nav mode" (if the departure clearance involves flying routing that is programmed into the FMS - PNF selects NAV in the flight director)
Passing 400 ft:
PF: "Autopilot on" (PNF engages autopilot; you're not allowed to engage autopilot below that).  Hands off the controls.
Passing 1000 ft, the PF dials up the speed bug on the flight director, typically 200 kt, and lets the airplane accelerate and calls "Flaps X", and/or "Flaps up" as the retraction speeds are passed.
You then continue to 3000 ft and dial the speed up to the normal departure climb speed, usually 230 to 250kt and off you go.

There are quite a few V-Speeds, not all are spoken during takeoff though
You do say:
(In some companies: "80 knots" - To inform the PF about the speed)
V1 - The speed above which you are not allowed to abort the takeoff under no circumstances.
Vr (Spoken "Rotate") - The speed at which the pilot pushes the nose upwards in order to generate lift
(In most companies: "positive climb" - To inform the PF that the aircraft is climbing with a positive speed and it is secure to retract the gear)


text:
Are there efficiency gains with quiet supersonic technology?
I was reading about the Nasa X-59 a low supersonic noise test aircraft which is nearing the start of flight testing, and it occurred to me that I don't understand the relationship between sonic boom creation, drag and other aspects of aerodynamics. Specifically, I am curious as to whether decreasing sonic boom has any impact on drag, and whether a shape that reduces boom may also reduce the fuel consumption required for supersonic flight.

Weaker shockwaves will reduce the amount of drag on the aircraft (unless in some very specific circumstances). Shockwaves cause a pressure jump, and if that pressure jump is on the front of the aircraft then that will cause a pushing force backwards. (Posting this as a comment because it doesn’t 100% answer your question)

Not really. It can be a side effect, but not the primary goal.
QSST research is primarily focused on directing most of the sonic boom upwards, avoiding impact on the ground. Weakening the boom itself, by making the aircraft closer to a more elongated Sears-Haack body, is one way to do it, and that also decreases drag, but it's only one of the ways used.
The lowest-drag shape is a thin spindle with full-length delta wings. Low sonic boom shapes try to keep a flatter bottom to spread out the impact.
If you consider drag per passenger, the complex shapes used in QSST research are likely to increase it above that of the Concorde, the Tu-144, or even the hypothetical Boeing 2707, since they can fit much fewer people in a similar-sized plane. Older SST projects were about "how can we make a supersonic plane economical for the public", new ones are about "how can we make supersonic flight permitted over land at all?"
Overall, the idea of public supersonic travel is in less demand now. The rest of the world failed to keep up with the advent of Mach 0.7 travel, much less supersonic. On almost any air trip today, one spends more time packing, driving to the airport, standing in lines, waiting for boarding, boarding, waiting for the plane to take off, and then the same in reverse, than actually flying.
That and reliable video conferencing make flight speed less relevant for most traveling public. even for the relatively well-off. Supersonic L/D will always be lower than subsonic, like a best-case of 7:1 vs 20:1. So it will always consume a lot more fuel and cost more.
The result is that modern supersonic transport research is aimed at low-volume private supersonic jets for the 0.0001%, not at large mass-produced aircraft. And smaller size, in itself, makes low sonic boom flight a lot more attainable. Fuel consumption is important so far as lower fuel flow allows for more range.

Fine answer! I might add that the elongated body will increase mass and, therefore, the need for lift creation. That in itself will cause stronger shocks, unfortunately in the downward direction.

Very nice answer

Thinking about this, I would think that having a plane deflect the shockwave downward would generate lift, and deflecting it upward would generate reverse lift.

Most of the things that cause sonic boom also cause drag, so reducing sonic boom and reducing drag are correlated in first order effects.
However, when it comes to subtleties, this is not the case.  An optimum shape from the perspective of sonic boom is not an optimum shape for drag.
So, the X-59 will be pretty low drag -- but not as low drag as it would be if the experiment was to fly the aircraft with the lowest drag instead of fly an aircraft with a tailored boom footprint that meets certain noise requirements.


text:
Who else is using electro-thermal wing anti-/de-icing apart from the 787?
I am researching into deicing technologies for the future, but apart from Boeing with Ultra/GKN, no one seems to be picking this technology up and being competitive. Any one know why this is? Is it an expensive development? Risky?
Is it on any aircraft manufacturer's roadmaps?

How many new aircraft have been designed since the 787 was released? If this technology was developed for the 787 (don't know, just speculating) it will take time to work its way into other new designs, and it would require a fair bit of recertification effort to retrofit it into existing designs. This work would cost time and money for little gain since all "modern" currently flying commercial aircraft already have a deicing system in place.

I fail to see what is exactly new in the B787 de-icing system, except for the way it is manufactured (spraying metallic layers onto the composite structure).
Electric heating is the most obvious and straightforward method of de-icing, and the least energetically efficient at that. It is much more efficient to break the ice rather than to melt it - in terms of the energy required. Even B787 with its sheer electric supply can't afford anti-icing (that is, constant heating to prevent ice formation), and de-icing power consumption is 45-75 kW.
Perhaps most Russian (larger) aircraft had electrical wing de-icing system: from Tu-95 (1952) to Il-18 (1957) to Tu-154 (1968) (I could give specific links but they are in Russian). Typically, they work in sections to reduce power demand, and consist of heating wires (rather than layers like on 787) that melt the ice.
Later aircraft such as Il-86 (1976) and -96 had a more advanced electric impulse system, which creates mechanical impulse on the leading edge with induction coils. This deforms the skin for a very brief moment to break the accumulated ice.

The F-35 and V-22 also use the same kind of blended electric heating pads as an anti/deice method. According to this article the conductive material that is used to make the heating units is applied during layup of the composite material for the wing. Thus it might not work on metal wing aircraft as most modern airliners are.
There is also the consideration of certification, which in aviation is a very important factor. Once an airframe is certified in a given configuration it may not be financially logical to certify some new part for a system that is already well in place and working.
Also as noted in this question, the 787 lacks the bleed air system needed to drive a classical anti-ice system so another solution is needed. But it still uses engine bleed for engine cowl and nacelle anti-ice.

Fokker 28 MK 100 has leading edge electrical anti ice system.

Welcome to Aviation.SE! You should add some details and sources to your answer to improve it.

Apparently electrothermal anti-ice systems are more energy efficient – about 35% better efficiency – than using HP compressor bleed air channeled through pipes to the leading edges of the lifting surfaces.  See this article.
https://www.aviationpros.com/article/12414609/electrification-and-e-flight-part-4-boeing-is-on-the-way-to-a-more-electric-future
I was not aware that Boeing was using electrothermal anti-ice systems on the 787.   They have been common in general aviation for sometime. Some examples are the Kelley ThermaWing used on some singles and light twins.  But yeah that’s the first time I’ve ever heard of such a system being used on an application that large.
This I believe goes back to the use of a uniform electrification in the aircraft.  Just about everything on the airplane is powered by its generators, including the flight controls hydraulics and other systems. If you start off with that plan for an aircraft like that it would make more sense to install electrothermal anti-ice systems on the wings as opposed to a separate, and dedicated bleed air system.


text:
How do I determine the engine thrust required to give a specific climb rate?
New pilot here and I am playing around with a flight simulator game for the B737-800. I need some help understanding where/how one can find out if one has enough engine thrust (%N1) to meet a required climb gradient in feet per minute, not in degrees.
If an airport has a SID that requires, let's say, 1100 feet per minute climb how do I know that the thrust setting (%N1) that I get from the OPT program is enough to give me that 1100 feet per minute when I takeoff? Where do I find that information? Is it in the OPT or is it in performance manuals and, if so, which performance manual? Please explain it in simple terms and with references. Thank you.

Well, if you are able to figure out a climb gradient in degrees, and know the resulting airspeed, and know the wind conditions (how much of a headwind you are flying into), it should be little more than trigonometry figuring out your climb rate in feet per minute instead. Is this what you're asking how to do?

No, my question is how do I know that the N1 that I get from the OPT is enough thrust to meet the required climb gradient in feet per minute published on the SID?


text:
Who defines the callsign for radio communication?
I started flying with VATSIM and but I couldn’t find a proper answer to this question online. Who defines a callsign for a plane in a given flight? Is a callsign set to a airplane? Is it related to the letters on the fuselage?

See Do flights of a specific callsign always depart and arrive at the same airports? (full disclosure: the accepted answer is my own) and to a lesser extent Can the airport name be omitted when contacting ATC if the frequency is not used by any other nearby airports?

See also When must full aircraft registration be used as radio callsign?

"VATSIM is the Virtual Air Traffic Simulation network, connecting people from around the world flying online or acting as virtual Air Traffic Controllers." In small GA planes, call sign is the tail number of the plane, often combined with airplane type. Ex: N12345, Cessna Cardinal, then Cardinal 12345 after comms are established. Then often shortened to just 345 when acknowledging an ATC request such as a frequency change if a similar tail number is not on the air at the same time. For airlines, see other replies.


text:
What should a pilot do upon reaching a Missed Approach Fix when holding instructions are not given?
Typically, Missed Approach Procedures end with a hold at the Missed Approach Fix. This is written in the textual procedures as something like "direct ABC VOR and hold." The graphical section also depicts the Missed Approach Fix, and the holding pattern relative to that fix, including the inbound course, inbound radial, and outbound course.
However, the ILS 20R approach at John Wayne Airport (KSNA) has only a fix as the last element of the Missed Approach Procedures. The textual procedures say:

Climb to 3000 on I-SNA LOC south course (196°) to MINOE INT/I-SNA 10.9 DME

The graphical representation of the Missed Approach Fix only shows the radials and DME used to identify the fix. It does not have a depicted holding pattern.

What should a pilot do upon reaching MINOE, in absence of other ATC instructions?

Is there an approach procedure starting at MINOE?

@J.Hougaard there are multiple approaches to KSNA from MINOE. However, they are all for runway 2L, not 20R. Two of them have circling minimums, though they are higher that the S-ILS 20R minimums on the ILS 20R approach.

@BillyClarke Out of curiosity,.are you asking because you found yourself in that situation? Missed approach, headed to MINOE and no one told you what to do next? That would be highly unusual considering how busy KSNA is.

@JuanJimenez yes, but only virtually. For purposes of IFR training, I was flying this approach on PilotEdge, went missed, and realized I would not have known what to do when I got to MINOE. The virtual controller gave me vectors for another approach, but I am interested to know what the correct full missed approach procedure is. Regardless of the improbability of needing to fly the full missed approach procedure, we have holds at the missed approach fix for a reason, and I’m wondering why it’s not depicted or described here.

@BillyClarke Yes, except we also don't have holds for good reasons too. The only way to fly holding patterns with RNAV that generally doesn't have holding pattern capability is manually. In that case the RNAV will only give you guidance for the inbound track, the rest is up to you. Were you specifically practicing an RNAV approach? What the controller did is what would be expected if you were.

The clip doesn't show it, but you must be looking at an RNAV approach chart for 20R. The ILS charts for 20R show the holding pattern in the plates. Since RNAV states "Radar Required" if the pilot doesn't get further instructions he/she should immediately ask for them.

I am looking at the ILS Rwy 20R at KSNA, not the RNAV approach chart. It has a holding pattern at the alternate missed approach fix, but not the regular missed approach fix.


text:
What is the critical altitude?
What is the definition of critical altitude and why is important to know in Vmc graph? Also, is there any critical altitude in the Piper PA-44 Seminole?

Do you have a copy of this Vmc graph? It may help get a more definite answer.

Critical altitude is the maximum altitude where the engine turbochargers (or turbonormalizers) can maintain sea level standard pressure to the engines. Above the critical altitude the engines will produce less power, although still delivering more power than an normally aspirated engine at the same air density.


text:
Why is trim for take off affected to Vmc(Speed maintain control)?
I am studying in Vmc part, but I have hard time to understand that trim for take off is affected to Vmc. How and why does it make Vmc speed increase?

What aircraft? This isn't always the case.

The trim setting doesn't increase or decrease Vmc speed itself.  I suspect your question is actually "what is the take-off trim setting's relationship to Vmc".
The term "trim", more or less referring to a state of aerodynamic equilibrium in the balance of pitch related forces, and such equilibrium being achieved at a given speed for a given weight/power/thrust configuration, you trim to a speed.  Trim speed is the speed the airplane will seek without physical intervention by the pilot or autopilot, for a given all up weight, CofG location, and power setting (I've always called the trim wheel a "hands free speed setting dial").
Trim settings for takeoff in multi-engine airplanes can normally be expected to be something at or close to single engine climb speed (blue line) in a piston twin, or at or close to V2, or single engine safety speed, in a transport airplane.
The idea is to have the airplane configured so that it will naturally seek a desired speed, or reasonably close to it, without control input, and reduce the workload on the pilot during periods of excitement.  To the extent that the trim setting is related to Vmc, it's to achieve this speed margin as determined by the manufacturer.

Elevator Trim does not change the Minimum Control Speed(Vmc). It is variables such as engine power, weight and balance, and center of gravity that can cause changes to Vmc.
Those variables can also mean changes to the correct elevator trim settings for takeoff.


text:
Why do some airplanes have their winglets at different angles?
While travelling recently a friend of mine noticed that the tips of the wings on some planes were at different angles on the left and the right hand sides of the plane.
Is this a thing and what is the reason for this?
Some googling and searching on this site did not reveal an answer.

It's possible that when looking out the windows of the plane from his seat, the winglets appeared to be at different angles due to her different viewing angle from one side of the plane. The closer he was to one window the farther she was from the other and that parallax could have made a difference.

@FreeMan - He was looking at other planes, from straight ahead or behind, not the plane we were in. The angles were obviously different on the different wings on least two planes he saw.

Winglets are symmetric, meaning they are the same shape, size and angle on both sides of the airplane. Different shapes and/or angles would mean the wings would have different aerodynamic properties, i.e. they'd fly differently from one another, which is generally a bad thing. It's probably been done for testing purposes, but not in production aircraft.
It's possible that your friend noticed that different makes and models of airplane have different winglets. Some look like this:

Some look like this:

There's other shapes too. Viewed from different angles it's possible they may look like different shapes, but they're going to be the same even if it doesn't seem that way.

He was looking at the planes from straight ahead or behind. The angles of the winglets were obviously different on the different wings on least two planes he saw.

Perhaps that's how it looked to him @Lizzan, but it's not the case, winglets are symmetric.

Sure, that makes the most sense, which is why he was so surprised to see it. I'll keep this question open for a while longer in case someone else knows of an exception.

I'm accepting this now as I've been on a trip and watched some winglets on my own. My first instinct on seeing a plane with them was that they were indeed different, but as we travelled behind the plane the opposite winglet seemed to be pointing almost inwards to the first I saw. It seems to be a powerful optical illusion unless you are watching from perfectly straight ahead or behind.


text:
What are ARTCC, RCO and FSS and what are differences?
I am confusing what ARTCC, RCO and FSS. and also what do they do?
Do they control air traffic by communicating with pilots?
Also, do they offer WX information in air born?

ARTCC or Air Route Traffic Control Center:

Does control traffic, generally in larger areas and above FL180 (Class A airspace)
Will broadcast some weather info and provide advisories

ARTCCs broadcast a Severe Weather Forecast Alert (AWW), Convective
  SIGMET, SIGMET, or CWA alert once on all frequencies, except
  emergency, when any part of the area described is within 150 miles of
  the airspace under their jurisdiction

RCO or Remote Communication Outlets:

Extends the range of FSS broadcasting ability
Many are being shut down

The remaining RCOs are of two types: 1,223 RCOs that allow pilots to
  contact flight service and receive transmissions over a common
  frequency; and 398 RCOs over which pilots can transmit—usually on
  122.1 MHz—and monitor flight service’s response on the frequency of a co-located VOR.

FSS or Flight Service Stations:

Flight Service Stations (FSS) are air traffic facilities that
  communicate directly with pilots to conduct preflight briefings,
  flight plan processing, inflight advisory services, search and rescue
  initiation, and assistance to aircraft in emergencies. FSS also relay
  Air Traffic Control clearances, process Notices to Airmen (NOTAMs) and
  provide updates on aviation meteorological and aeronautical
  information.

Provides inflight weather, preflight planning and clearances and takes NOTAMS. Does not control traffic in the air but is involved in dispatching instructions (clearances) prior to takeoff.
Offering weather is a bit tricky. Controllers and those on the other end of the radio all have access to different levels of weather information and weather radar. Many will provide some level of information if asked. What they will provide is perhaps worthy of its own question here.


text:
Can only victor way be used for route in cross country?
In IFR low-en route chart, there are many ways related to victor ways. Do I have to select the route for cross county? Or, Can I choose the ways between victor ways?

Are you asking about a specific country? In some parts of the world (e.g. Asia) routes are very strictly controlled; in others (e.g. United States) there's a lot more flexibility.

You just use (starting waypoint)  DCT  (ending waypoint) in your flight plan (DCT = Direct) and submit that.  It's up to ATC to approve that routing and you'll find out when you are issued your clearance.
Especially at lower altitudes it's likely you'll be cleared as filed, but there's always a chance they'll shift your route a bit to improve traffic flow for whatever reason, adding waypoints or moving you to an adjacent V airway, doing their best to minimize any increase in your distance.

You can request any way you want. The actual IFR clearance given may be something else altogether, depending on other traffic, and possibly even GPS direct from your current location to a waypoint near to the intended point of landing if conditions are favorable.

Your routing will also be impacted by where you are starting from. I depart from a non-towered airport, typcially with a void-time clearance (have to be airborne and contact ATC within a time-limit). The clearance is usually to fly some heading where the Class B overlying the airport can confirm it's me they see on radar, then a heading change or two before being released to a first waypoint farther along on my planned route.  If I can depart VFR instead and get away from the Class B before asking for IFR, there is a lot less fooling around to start the trip.